Jump to content
Sign in to follow this  

New Rotax glasspack muffler on - now backfire

Recommended Posts

The bike is a 95 MZ SilverStar with the Rotax 504E engine. I found a new Ron Woods low pipe MZ glasspack muffler, and installed it, pic attached. Lots more grunt, no stumbling, idles well at ~1200 RPM, and lot more noise which I kind of expected. 👍 I still have the stock Bing carb, and am getting noticable afterfire on deceleration through the new muffler. I was not getting it with the ultra-quiet stock can. Or maybe it was muffled out and I just couldn't hear it. I had rebuilt the stock Bing CV carb and replaced all the o-rings and diaphragm. I moved the needle back from the #4 to the #3 stock position (lowering it), didn't help with the backfiring. I've researched and have read that pilot jet needs to be larger for this problem, but on my Bing carb parts breakdown there's no mention of a pilot jet. What does Bing call the pilot jet, the idle jet? I'm not even sure if the backfire is being caused by carburation, but I suspect it is. All jetting at present on the Bing is stock, and the engine (9000 km on it) runs great in all respects except for the popping thru the can when on decel. I have checked for intake and exhaust leaks also and all appears well.

Also, I've never checked the valve adjustment since I've had the bike. Could this also be causing the backfire? I know it's hard to diagnose via email as the possible causes are numerous, but I'd sure appreciate some advice as to where to start. Thanks; Don

Small1.jpg

Edited by comanche91

Share this post


Link to post
Share on other sites

Yes, that's true, but looking for a logical troubleshooting procedure. I pulled the plug and it looks as it should. 👍

Share this post


Link to post
Share on other sites

My Rotax would pop on decel when the idle circuit or needle setting was lean. I would guess the new can has leaned it out a bit. Think about decel, the throttle is closed. I would try a little richer on the fuel screw first. Not sure about a bing carb though. Mine had Delorto.

Share this post


Link to post
Share on other sites

I've tried the fuel screw first thing gorgon, and it's a bit less pop toward the richer end, but still unsat. Called Bing and they recommended this procedure, one at a time:

1. Install new 2.68 needle jet (next size up)

2. Raise the needle one notch

3. Install new 48 idle jet (one size up)

4. Install new 130 main jet (also one size up)

Kind of goes along with what you said. 👍 I've ordered the parts and will give it a go. But first will check the valve clearances since I haven't done it yet. -Don

Share this post


Link to post
Share on other sites

FIXED! A larger needle jet (2.68) and idle jet (48) from Bing, then readjusting the mixture screw a bit richer cured it. I still have slight popping sounds when coasting down a steep grade in 3rd gear that sound good, but no more of the ear splitting afterfire bangs like before. Thanks for the help on this gorgon you were was spot on. -Don

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...